Methods of maintaining droplet transport

Abstract

The invention provides a method for reducing or preventing droplet pinning as the droplet is transported across a boundary between a ground electrode region and a non-ground electrode region on a droplet actuator. The invention also provides a method for reducing or preventing droplet super-movement as the droplet is transported across a boundary between a ground electrode region and a non-ground electrode region on a droplet actuator.

1 . A method for reducing or preventing droplet pinning as the droplet is transported across a boundary between a ground electrode region and a non-ground electrode region on a droplet actuator, comprising:
 a. providing the droplet actuator, wherein the droplet actuator comprises:
 i. a bottom substrate and a top substrate separated to form a droplet operations gap; 
 ii. a ground electrode disposed on a portion of the top substrate; and 
 iii. a linear arrangement of a plurality of droplet operations electrodes disposed on the bottom substrate, wherein the plurality of droplet operations electrodes spans the boundary between the ground electrode region and the non-ground electrode region; 
   b. positioning an elongated droplet on more than one of the plurality of droplet operations electrodes, wherein the elongated droplet is positioned atop at least one droplet operations electrode in the ground electrode region and at least one droplet operations electrode in the non-ground electrode region;   c. activating the at least one droplet operations electrode in the non-ground electrode region; and   d. activating the next droplet operations electrode of the linear arrangement in the non-ground electrode region and deactivating the at least one droplet operations electrode in the non-ground electrode region;   
       wherein the elongated droplet is transported out of the ground-electrode-region and into the non-ground electrode-region. 
     
     
         2 . The method of  claim 1 , wherein the ground-electrode-region comprises the ground electrode, and wherein the ground electrode comprises a layer of electrically conductive material. 
     
     
         3 . The method of  claim 2 , wherein the layer of electrically conductive material comprises poly(3,4-ethylenedioxythiophene) (PEDOT). 
     
     
         4 . The method of  claim 1 , wherein the non-ground electrode-region does not comprise the ground electrode. 
     
     
         5 . The method of  claim 1 , wherein a hydrophobic layer is disposed on the surface of the top substrate facing the droplet operations gap. 
     
     
         6 . The method of  claim 5 , wherein the hydrophobic layer comprises an amorphous fluoropolymer. 
     
     
         7 . The method of  claim 1 , wherein the hydrophobic layer is a sufficient thickness to facilitate droplet transport across the boundary between the ground-electrode-region and the non-ground electrode-region. 
     
     
         8 . The method of  claim 7 , wherein the thickness of the hydrophobic layer is about 5 μm. 
     
     
         9 . The method of  claim 1 , wherein the top substrate further comprises a dielectric layer. 
     
     
         10 . The method of  claim 9 , wherein the dielectric layer comprises polyimide. 
     
     
         11 . The method of  claim 1 , wherein activation of droplet operations electrodes comprises activation using an alternating current. 
     
     
         12 . The method of  claim 1 , wherein activation of droplet operations electrodes comprises activation using a direct current. 
     
     
         13 . The method of  claim 1 , further comprising providing a path of conductive material on the top substrate that spans the boundary between the ground electrode region and the non-ground electrode region of the droplet actuator. 
     
     
         14 . The method of  claim 13 , wherein the path of electrically conductive material comprises poly(3,4-ethylenedioxythiophene) (PEDOT). 
     
     
         15 . The method of  claim 1 , wherein the path of electrically conductive material is of a width sufficient to facilitate droplet transport across boundary between the ground electrode region and the non-ground electrode region of the droplet actuator. 
     
     
         16 . The method of  claim 15 , wherein the width of the path of electrically conductive material is about 120 μm. 
     
     
         17 . A method for reducing or preventing droplet super-movement as the droplet is transported across a boundary between a ground electrode region and a non-ground electrode region on a droplet actuator, comprising:
 a. providing the droplet actuator, wherein the droplet actuator comprises:
 i. a bottom substrate and a top substrate separated to form a droplet operations gap, wherein the top substrate is deionized; 
 ii. a ground electrode disposed on a portion of the top substrate; and 
 iii. an arrangement of droplet operations electrodes disposed on the bottom substrate; and 
   b. transporting the droplet out of the ground electrode region and into the non-ground electrode region by electrowetting.   
     
     
         18 . A method for reducing or preventing droplet super-movement as the droplet is transported across a boundary between a ground electrode region and a non-ground electrode region on a droplet actuator, comprising:
 a. providing the droplet actuator, wherein the droplet actuator comprises:
 i. a bottom substrate and a top substrate separated to form a droplet operations gap, wherein a portion of the top substrate facing away from the droplet operations gap is coated with a conductive coating; 
 ii. a ground electrode disposed on a portion of the top substrate; and 
 iii. an arrangement of droplet operations electrodes disposed on the bottom substrate; and 
   b. transporting the droplet out of the ground electrode region and into the non-ground electrode region by electrowetting.   
     
     
         19 . The method of  claim 18 , wherein the conductive coating comprises a continuous layer on the top substrate. 
     
     
         20 . The method of  claim 18 , wherein the conductive coating comprises an array of islands of conductive material on the top substrate. 
     
     
         21 . The method of  claim 18 , wherein the conductive coating comprises lines of conductive material in a grid pattern on the top substrate. 
     
     
         22 . The method of  claim 1 , wherein the conductive coating comprises Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate. 
     
     
         23 . A microfluidics system programmed to execute the method of  claim 1  on the droplet actuator. 
     
     
         24 . The microfluidics system of  claim 23 , wherein the droplet actuator is coupled to a processor that executes program code embodied in a storage medium for executing the method. 
     
     
         25 . A storage medium comprising program code embodied in the medium for executing the method of  claim 1  on the droplet actuator. 
     
     
         26 . A microfluidics system programmed to execute the method of  claim 17  on the droplet actuator. 
     
     
         27 . The microfluidics system of  claim 26 , wherein the droplet actuator is coupled to a processor that executes program code embodied in a storage medium for executing the method. 
     
     
         28 . A storage medium comprising program code embodied in the medium for executing the method of  claim 17  on the droplet actuator. 
     
     
         29 . A microfluidics system programmed to execute the method of  claim 18  on the droplet actuator. 
     
     
         30 . The microfluidics system of  claim 29 , wherein the droplet actuator is coupled to a processor that executes program code embodied in a storage medium for executing the method. 
     
     
         31 . A storage medium comprising program code embodied in the medium for executing the method of  claim 18  on the droplet actuator.